Cast alloy for valve seat insert

ABSTRACT

The present invention relates to a cast alloy for a valve seat insert, which has an excellent wear resistance for automobile engines using non-leaded gasoline. The alloy according to the present invention is a phosphoruscontaining precipitation-hardening type austenitic alloy. It can reach the hardness at ordinary temperature of more than HRC 40 by subjecting it to aging treatment after solution heat treatment. Accordingly, the alloy according to the present invention has such features that said alloy has an excellent creep resistance at high temperatures, further an excellent corrosion resistance, and an excellent wear resistance as a valve seat insert for automobile engines using non-lead gasoline. The present invention discloses that such excellent properties are obtained in the austenitic alloy having the following restricted chemical composition: (1) 0.80 to 2.50 % of C, (2) 0.20 to 3.0 % of Si, (3) 0.10 to 5.0 % of Mn, (4) 0.03 to 0.50 % of P, (5) 0.02 to 0.3 % of S, (6) 13.0 to 28.0 % of Ni, (7) 10.0 to 30.0 % of Cr, (8) 0.1 to 5.0 % of Mo, (9) 0.02 to 0.20 % of N, (10) 5.0 to 15.0 % of W, (11) 5.0 to 15.0 % of Co, and the remaining part consisting of iron and a slight amount of impurities.

United States Patent [191 Kusalta et al.

[ CAST ALLOY FOR VALVE SEAT INSERT [75] Inventors: Kunio Kusaka, Yokohama; Tomio Sekine, Kawasaki; Makoto Osawa, Tokyo; Yoshitoshi Hagiwara, Niiza; Yoshiaki Takagi, Kawagoe, all of Japan [73] Assignees: Tokushu Seiko Co., Ltd., Kawasaki;

Honda R&D Co., Ltd., Wako, both of Japan [22] Filed: Mar. 26, 1973 [21] Appl. No.: 344,583

[30] Foreign Application Priority Data Primary Examiner-Hyland Bizot Attorney, Agent, or FirmOblon, Fisher, Spivak, McClelland & Maier [4 1 Dec. 10, 1974 5 7 ABSTRACT The present invention relates to a cast alloy for a valve seat insert, which has an excellent wear resistance for automobile engines using non-leaded gasoline.

invention has such features that said alloy has an excellent creep resistance at high temperatures, further an excellent corrosion resistance, and an excellent wear resistance as a valve seat insert for automobile engines using non-lead gasoline.

The present invention discloses that such excellent properties are obtained in the austenitic alloy having the following restricted chemical composition: (1,) 0.80 to 2.50 of C, (2) 0.20 to 3.0 of Si, (3) 0.10 to 5.0 of Mn, (4) 0.03 to 0.50 of P, (5) 0.02 to 0.3 of S, (6) 13.0 to 28.0 of Ni, (7) 10.0 to 30.0 of Cr, (8) 0.1 to 5.0 of Mo, (9) 0.02 to 0.20 of N, (10) 5.0 to 15.0 of W, (11) 5.0 to 15.0 of Co, and the remaining part consisting of iron and a slight amount of impurities.

2 Claims, N0 Drawings CAST ALLOY FOR VALVE SEAT INSERT SUMMARY OF THE INVENTION The valve seat insert is a part playing an important role to retain airtightness within the cylinder by coming into impact and slide contact with the suction valve and exhaust valve at high temperatures. In the gasoline presently used, lead is added for the purpose of raising the octane value. When lead burns within the cylinder, it is converted into lead oxide, and a part of the thus produced lead oxide is adherence to the exhaust valve and the valve seat insert and functions as a lubricant.

Hertofore, a l C 8 Cr steel and a 1.5% C -13 Cr steel has been used for the valve seat alloy for automobile engines. In the case of using non-leaded gasoline, lead oxide which functions as a lubricant is not produced as a combustion product. Hence, the coefficient of friction between the exhaust valve and the valve seat becomes large, and it has been experienced that abnormal wear of valve seat occurs by the instantaneous deposition phenomenon due to the metal contact between the valve and the valve seat. Particularly, in the case of using an exhaust valve on the face of which stelite filling is carried out, the wear of the valve seat is remarkable.

As a result of exhaustive studies on the valve seat alloy, the present inventors have succeeded in obtaining an alloy having an excellent wear resistance as a valve seat insert for automobile engines using non-leaded gasoline by adding W and Mo to a high-carbon Cr Ni austenite alloy whose matrix is enhanced by adding Co and N, and further adding P to said alloy to impart a precipitation-hardening property thereby im parting a wear resistance to said alloy.

Said alloy has the following chemical composition.

DETAILED DESCRIPTION OF THE INVENTION In the alloy according to the present invention, C I

combines with Cr to produce a hard carbide to enhance wear resistance, and is solidly dissolved in austenite to improve the strength of the alloy. However, when less than 0.80 of C, is present the wear resistance of the alloy is inferior and when more than 2.5 of C, is prescm, the toughness of the alloy is lowered. Therefore, C is added thereto in the range of from 0.80 to 2.5

Si improves acid resistance and castability. However, at less than 0.2 of Si, the fluidity of the molten bath is inferior, and at more than 3 of Si, the toughness of the alloy is lowered. It was, therefore, added thereto in the range of from 0.2 to 3.0 Mn is added to the alloy as a deoxidant and is effective for enhancing austenite formation. It was, therefore, added thereto in the range of from 0.10 to 5.0

P is necessary for imparting precipitation-hardening properties to the alloy. However, at less than 0.03 of P, its effect is poor. At more than 0.50 of P, the toughness of the alloy is lowered. It was, therefore, added thereto in the range of from 0.03 to 0.50

S produces a sulfide. It is effective to improve lubrication properties because the sulfide is present in the form of a fine granule. It is added to improve machinability of the hardened steel after aging treatment. However, at less than 0.02 of S, its effect is poor and at more than 0.30 thereof, toughness of the alloy is lowered. It was, therefore, added thereto in the range of from 0.02 to 0.30

Ni austenitizes the structure of the alloy, improves corrosion resistance, and increases strength at ordinary and high temperatures, and simultaneously is effective to retain toughness. Ni further functions to improve fitting to the valve face. However, at less than 13 of Ni, its effect is poor, and even at over 28 it does not contribute to increase the effect. It was, therefore, added to the alloy in the range of from 13.0 to 28.0

Cr is effective for producing a film on the surface, and improves acid resistance and wear resistance. However, at less than 10.0 of Cr, the acid resistance, wear resistance and strength are not satisfactory. At more than 30 of Cr, toughness is deteriorated and machinability is lowered. Therefore, it was added to the alloy in the range of from 10.0 to 30.0

M0 is effective for increasing the strength at high temperatures, enhancing the matrix, and improving wear resistance. At less than 0.1 of Mo,its effect is poor, and at more than 5 of Mo. the improvement in the effect is slight and cost becomes high. Therefore, it was added to the alloy in the range of from 0.1 to 5.0 1

N is effective in increasing hardness by solidly dissolving in austenite, increasing strength at high temperatures and improving wear resistance. Also, it is effective in the improvement of fitting. At less than 0.02 its effect is small. Also, at more than 0.20 toughness and castability are lowered. Therefore, it was selected to be in the range from 0.02 to 0.20

W produces a hard carbide and is effective in pulverizing the structure and improving the wear resistance. At less than 5.0 its effect is poor and at over 15 the effect is poor. It was, therefore, selected to be in the range from 5.0 to 15.0

V produces a hard carbide and is effective in pulverizing the structure and improving the wear resistance. At less than 0.1 its effect is poor and even at more than 4 the effect is not so large. Therefore, it was selected to be in the range from 0.1 to 4.0

Co is effective for enhancing matrix, increasing the strength at high temperatures, improving of fitting and decreasing wear of the valve seat. At less than 5.0 of Co, its effect is poor, and at more than 15.0 of Co, the improvement in the effect is slight. Therefore, it was added to the alloy in the range of from 5.0 to 15.0

The function of the alloy according to the present invention will be explained with reference to the test results. Table 1 shows the chemical compositions of the samlples. Sample A in the Table is the steel for used in the present valve seat. Samples B and C are alloys according to the present invention.

Chemical composition of Alloys tested Table 1 Alloy Chemical Composition No C St Mn P S Ni Cr N Mo W Co V A .20 0.40 0.65 0.010 0.05 8.9 B 1.92 1.39 1.11 0.20 0.20 20.5 22.0 0.10 2.6 6.1 12.1 C .91 1.40 1.10 0.21 0.19 20.2 23.1 0.11 2.5 6.2 11.9 i 2.6

Aged hardness Table 2 Alloy No. Heat treatment Rockwell C Hardness A 950C Oil Ouenched, 600C 1hr Air cool 37.0 B 1 100C Oil Quenched, 700C 2hr Air cool 41.0 C 1100C Oil Quenched. 700C X 2hr Air cool 41.0

Table 2 shows the heat treatment hardness. The sam- Mean wear Length of valve seat insert after 100 hr operation Table 3 Alloy No. Mean wear length (pl/hr) A 3.0 4.2 B 0.10 0.15 C 0.08 0.14

According to these results, the alloys 13 and C according to the present invention have exceedingly small mean wear lengths in valve seats, and hence have very excellent functions as valve seats for non-leaded gasoline.

As has been explained in the foregoing, in the alloy according to the present invention, the casting thereof is subjected to solution heat treatment at 1 C., hardness after subjecting the casting to aging treatment at 700C. for 2 hours is raised approximately to H C 41. Thus, the alloy according to the present invention is extremely superior in wear resistance, oxidation resistance, and corrosion resistance fitting to the value face and thus it has excellent capacities as a valve seat for automobile engines using non-lead gasoline.

What we claim is 1. A high-efficiency alloy for a valve seat insert of ex cellent durability, consisting essentially of in weight ratio 0.80 to 2.50 of C, 0.20 to 3.0 of Si, 0.10 to 5.0 of Mn, 0.03 to 0.50 of P, 0.02 to 0.30 of S, 13.0 to 28.0 of Ni, 10.0 to 30.0 of Cr, 0.1 to 5.0 ofMo, 0.02 to 0.20 of N, 5.0 to 15.0 of W, 5.0 to 15.0 of Co, and the remaining part consisting of iron and a slight amount of impurities.

2. A high-efficiency alloy for a valve seat insert of excellent durability, consists essentially of in weight ratio 0.80 to 2.50 of C, 0.20 to 3.0 of Si, 0.10 to 5.0 of Mn, 0.03 to 0.50 of P, 0.02 to 0.30 of S, 13.0 to 28.0 of Ni, 10.0 to 30.0 of Cr, 0.1 to 5.0 of Mo, 0.02 to 0.20 of N, 5.0 to 15.0 of W, 5.0 to 15.0 of Co, 0.1 to 4.0 of V, and the remaining part consisting of iron and a slight amount of impurities. 

1. A HIGH-EFFICIENCY ALLOY FOR A VALVE SEAT INSERT OF EXCELLENT DURABILITY, CONSISTING ESSENTIALLY OF IN WEIGHT RATIO OF 0.80 TO % OF C, 0.20 TO 3.0% OF SI, 0.1 TO 5.0% OF MN, 0.03 TO 0.50 % OF P, 0.02 TO 0.03% OF S, 03.0 TO 28.0% OF NI, 10.0 TO 30.0 % OF CR, 0.1 TO 5.0% OF MO, 0.02 TO 0.20% OF N, 5.0 TO 15.0 % OF W, 5.0 TO 15.0% OF CO, AND THE REMAINING PART CONSISTING OF IRON AND A SLIGHT AMOUNT OF IMPURITES.
 2. A high-efficiency alloy for a valve seat insert of excellent durability, consists essentially of in weight ratio 0.80 to 2.50 % of C, 0.20 to 3.0 % of Si, 0.10 to 5.0 % of Mn, 0.03 to 0.50 % of P, 0.02 to 0.30 % of S, 13.0 to 28.0 % of Ni, 10.0 to 30.0 % of Cr, 0.1 to 5.0 % of Mo, 0.02 to 0.20 % of N, 5.0 to 15.0 % of W, 5.0 to 15.0 % of Co, 0.1 to 4.0 % of V, and the remaining part consisting of iron and a slight amount of impurities. 